<!DOCTYPE html>
<meta charset="utf-8">
<style>
html, body {
    margin: 0;
}
div, section {
    position: absolute;
}
div {
    width: 300px;
    height: 32px;
    right: 0;
    background: green;
}
section {
    left: 0;
    right: 300px;
    height: 64px;
    background: blue;
}
#a {
    top: 0;
}
#b {
    top: 64px;
}
</style>
<div></div>
<section id=a></section>
<section id=b></section>

